The present invention relates to an optimal image-quality selection apparatus for selecting an optimal quality of an image in an optical reader and more particularly, relates to an apparatus for selecting an optimal depth of color of the image.
In a conventional optical reader, the following methods are available as a method of digitizing a video signal output from a scanner to a processor: a method of digitizing a video signal with reference to fixed depth levels; a method of digitizing a video signal on the basis of depth levels of a background color; a method of digitizing a video signal by using a space filter so as to correspond to a change in the depth of color of a character, graphic, or the like; and a method of processing a video signal as a multi-level signal.
It is difficult to apply the method of processing the video signal as the multi-level signal to a character reader used for reading addresses on postal matters because of following reasons. That is, there are many kinds of envelopes having different colors of various depths and various thicknesses of the materials thereof. When the thickness of the material of the envelope is small, some pattern printed on the envelope with a light color and content of the envelope may be seen through. In addition, the addresses printed on the envelopes have various depths of color.
Accordingly, the video signal output from the scanner of the character reader has too broad range of depth level to be digitized as a multi-level signal. Therefore, the digitizing method on the basis of the background level or the digitizing method by the space filter have been employed.
However, when a depth level is set to read addresses which are printed with light characters, images including many noise components other than the addresses appear when the addresses are printed on envelopes having the small thickness. On the contrary, when the depth level is set not to detect the noise components, the addresses which are printed with light-color characters can not be read.